For a gallium nitride (GaN) based light-emitting diode (LED), a sapphire substrate is widely used. The sapphire substrate has poor thermal performance and electrical isolation. To improve the thermal and electrical properties of the GaN-LED, another substrate with higher thermal conductivity and electrical conductivity is bonded to the LED structure and then the sapphire substrate is removed. However, the removal of the sapphire substrate is a challenge since it may cause cracking of the LED structure and further lead to leakage current and device degradation. Therefore, methods and structures of GaN-LED devices are needed to address the above issues.